In image transfer processes which use two-sheet diffusion materials, a negative sheet or a donor sheet is exposed imagewise with a subject, wetted with a developing liquid or an activator and then pressed congruently onto a positive or receiver sheet. During the firm contact between the two sheets, an image-forming substance, for example a silver salt or a dye diffuses out of the imagewise exposed negative sheet into the positive sheet. A positive image is obtained after the sheets have been separated.
Various processes and apparatus are known for carrying out the image transfer process, in which either it is only the negative sheet which is exposed to a developer and the positive sheet is delivered dry through a second channel to the wetted negative sheet for pressing together, or both sheets are passed at the same time, but separately through a developer solution and are only brought together at pressing rollers where they are pressed together. Devices of this type are known, for example from U.S. Pat. No. 4,223,991 or from the publication Research Disclosure (December 1978. P. 32, No. 17,647).
These and other known devices suffer from the disadvantage that it is very difficult to guide the two sheets separately or together through the developer solution so that they are exactly congruent when pressed together by the pressing rollers. Thus, such devices do not allow borderless enlargements. The positive sheet has to be trimmed to the final size of the image.
Therefore, in order to compensate for the fitting inaccuracies caused by the devices, the positive sheets are cut larger in length (about 5 mm) than the appropriate negative sheets and are then trimmed all round after processing. Thus, apart from the additional working expense, a considerable loss of material also results.
Swiss Pat. No. 375,609 discloses a process and an apparatus for the development of reproductions, in which the exposed negative sheet is bonded at one of its edges to the corresponding edge of the positive sheet. The apparatus has a removable or pivotal part, on which the bonded edge is applied outside the apparatus and is guided thereby through the developer to the pressing rollers. In this process, both sheets are wetted with developer liquid.
The process and apparatus are very difficult to manage. The pivotal part is moistened with developer and it wets an area of the positive and negative sheets even outside the apparatus while the two sheets are being positioned on this part, so that the sheets may stick to the part, at least, at the contact points for a longer time to the developer liquid.
Thus, an object of the present invention is to provide a process and an apparatus of the initially mentioned type, with which it is easily possible to wet evenly a positive sheet and an exposed negative sheet with a developing liquid to transfer the image and to exactly guide and press the two sheets together so that the edges of these sheets are exactly congruent.